The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Telescoping assemblies such as disclosed in U.S. Pat. No. 5,465,854 are known. Generally, the telescoping tube assembly disclosed in this patent includes a first longitudinal tube section attached to a mounting platform and a second longitudinal section that telescopes relative to the first longitudinal tube section. Additional tube sections can be disposed within each other and within the second longitudinal tube section. Each longitudinal tube section includes a rigid support plate with a U-shaped housing having two spaced-apart longitudinal edges, which attach to the corresponding rigid support plate. Between each longitudinal section are linear bearings or wheels, which allow for the telescopic movement.
In one embodiment, the telescoping tube assembly operates vertically in that the longitudinal tube sections extend and retract downwardly from the first longitudinal tube section. The telescoping action is produced by a drum having a drive cable wrapped therearound and attached to the inner tube section. If the mast has more than one movable tube section, reeving cables or belts can be provided to control movement of each tube section. However, a disadvantage of the above-described assembly is that the use of drive cables limits operation to vertical deployment since the cables can not operate in compression, but only in tension.
In many applications, such as lifting or milling operations, it is necessary that the telescoping tube assembly be able to operate in the presence of compression and tension forces. Drive assemblies have been advanced for telescoping tubes or cranes that used elongated hydraulic cylinder units to extend and retract individual sections. However, as the telescopic assembly increases in size and weight and in the number of moveable sections, the size, weight, number and complexity of hydraulic cylinders increases accordingly. Similarly, other telescopic drive assemblies have used ball-screw assemblies to extend and retract each of the sections, but the size, weight, number and complexity of ball-screw assemblies also increases with the number of moveable sections.
There is thus an ongoing need to provide improved means to operate telescoping assemblies.